Typically 4 to 8 inches of gravel---packed with something heavy---then 4 inches of concrete---for a small job like that---a wheel barrow -hoe and bags of concrete mix would be the easiest.
Make your wood forms good and strong---buy some J-bolts to stick into the wet cement--they will help hold the block
Make your wood forms good and strong---buy some J-bolts to stick into the wet cement--they will help hold the block